SpaceX cargo capsule cleared for Space Station docking

Cape Canaveral, Florida: A cargo capsule owned by Space Exploration Technologies was cleared for a belated docking at the International Space Station on Sunday after engineers resolved a problem with the spacecraft's thruster pods, NASA said on Saturday.

The Dragon spacecraft, built and operated by privately owned Space Exploration Technologies, or SpaceX, missed its scheduled arrival on Saturday after problems surfaced with three of its four thruster rocket pods shortly after launch on Friday.

NASA flight rules require at least three pods to be operational before the craft would be cleared to approach the station, a $100 billion, permanently staffed research outpost that circles about 250 miles (400 km) above the Earth.

The capsule was launched aboard a SpaceX Falcon 9 rocket from Florida's Cape Canaveral Air Force Station on the second of 12 planned cargo runs to the station for NASA. After reaching orbit, the capsule ran into a problem starting its thruster systems.

Preliminary analysis showed a blockage in the pressurization system or a stuck valve was responsible, SpaceX founder and chief executive Elon Musk told reporters in a conference call Friday afternoon.

Engineers later resolved the problem by testing the valves and "pressure hammering" the lines. The troubleshooting worked, and Dragon fired its thrusters Friday evening to raise its altitude. Since then, the capsule has been tweaking its orbit to catch up with the station.

"Dragon's propulsion system is operating normally along with its other systems and ready to support the rendezvous," NASA wrote in a statement.

"SpaceX said it has high confidence there will be no repeat of the thruster problem during rendezvous, including its capability to perform an abort, should that be required," the US space agency said.

The capsule carries more than 2,300 pounds (1,043 kg) of science equipment, spare parts, food and supplies for the six-member station crew.

Dragon is expected to come within reach of the station's robot arm so astronauts aboard the outpost can latch on to a grapple fixture at 6:01 EST (1101 GMT) Sunday and berth the capsule at a docking port.

The capsule will be SpaceX's third spacecraft to visit the station. Following a test flight in May 2012, the company delivered its first load of cargo to the outpost in October under a 12-flight, $1.6 billion contract.

A second firm, Orbital Sciences Corp. is due to debut its space station freighter this year.

NASA turned to private companies for delivering supplies to the station following the retirement of its space shuttles in 2011. The agency hopes to buy rides commercially for its astronauts as well beginning in 2017.